The invention relates to chromatography columns and to methods of preparing chromatography columns.
Gas chromatography columns having a stationary phase consisting of a poly(ethyleneglycol), commonly abreviated as PEG, are known. Other names for PEG are poly(ethylene oxide) or poly(oxirane). Poly(ethyleneglycol)s exist in various forms, all of which are polymers comprising a plurality of repeat units having the formula:

A basic form of poly(ethyleneglycol) is a straight chain molecule having a hydroxyl group at each end and being represented by the formula:

This form will be referred to as diol poly(ethyleneglycol).
However, there are many other forms of straight chain poly(ethyleneglycol) in which one or both of the terminal hydroxyl groups of diol poly(ethyleneglycol) are chemically modified or replaced. Common forms are monomethoxy and dimethoxy poly(ethyleneglycol), in which one or both of the terminal hydroxyl groups of diol poly(ethyleneglycol) are replaced with methoxy groups. Another poly(ethyleneglycol), described by Glastrup in Polymer Degradation and Stability, 81 (2003) 273-278, has an additional methyl group inserted between a terminal hydroxyl group and the adjacent ether linkage of diol poly(ethyleneglycol). Dale et al, in Journal of Chromatography, 552 (1991) 161-167, discloses poly(ethyleneglycol)s in which antioxidant groups are introduced into diol poly(ethyleneglycol) by esterification of one or both terminal hydroxyl groups. Many other forms of straight chain poly(ethyleneglycol), having a wide variety of terminal groups, are also known. Terminal groups in a particular poly(ethyleneglycol) may be the same as one another or different.
Poly(ethyleneglycol)s can also be made in a branched form. A branched poly(ethyleneglycol) comprises two poly(ethyleneglycol) chains covalently linked to a common core. The preparation of branched poly(ethyleneglycol)s is well known and described in, for example, U.S. Pat. No. 5,183,660 and U.S. Pat. No. 5,932,462. The free terminals of a branched poly(ethyleneglycol) may be hydroxyl or other groups and they may be the same or differ from one another.
Poly(ethyleneglycol)s can also be made in multi-arm form. These have three or more “arms” each comprising a poly(ethyleneglycol) chain. Multi-arm poly(ethyleneglycol)s are described in, for example, U.S. Pat. No. 5,932,462. The free terminals of a multi arm poly(ethyleneglycol) may be hydroxyl or other groups and they may be the same or differ from one another.
Poly(ethyleneglycol)s can also be made in cross-linked form. One way of doing this is to chemically modify both hydroxyl groups of diol poly(ethyleneglycol) so that the modified terminals can be cross-linked to one another. As both terminals participate in cross-linking, an insoluble network of poly(ethyleneglycol) chains is formed. Cross-linking of polyethylene chains can also be achieved by controlled thermal treatment as described by Cardoso et al in Journal of Brazilian Chemical Society, Volume 11, No. 2 (2000) 191-194.
Straight chain, branched, multi arm and cross-linked forms of poly(ethyleneglycol), with a variety of terminal groups (where appropriate) can all be used for the stationary phase of chromatography columns, especially gas chromatography columns. It is also possible to use mixtures of the different forms of PEG as a stationary phase. In the case of cross-linked poly(ethyleneglycol)s, the poly(ethyleneglycol) may first be introduced into the column before the cross-linking takes place in situ. Poly(ethyleneglycol)s, in the various forms, make particularly useful stationary phases for gas chromatography, because they have good selectivity (that is to say the ability to separate) for polar compounds.
However, a problem with the use of poly(ethyleneglycol)s for the stationary phase in gas chromatography is that poly(ethyleneglycol)s tend to have undesirably low thermal stabilities. At the temperatures commonly used for gas chromatography, poly(ethyleneglycol)s tend to break down. Fragments formed from the thermal degradation of poly(ethyleneglycol)s in gas chromatography columns are detected by mass spectrometry and flame ionisation detection (which are the main methodologies used to detect analytes). The detection of fragments from the thermal breakdown of poly(ethyleneglycol) stationary phases by mass spectrometry or flame ionisation detection gives rise to background noise which may decrease the sensitivity of detection for the analytes.
Additionally, the thermal instability of a poly(ethyleneglycol) stationary phase can reduce the working lifetime and maximum allowed operating temperature of a gas chromatography column.
There have been a number of attempts to improve the thermal stability of poly(ethyleneglycol). The introduction of antioxidant groups into poly(ethyleneglycol) as described in the article by Dale et al referenced above, the introduction of a methylene group as described in the article by Glastrup referenced above, and the thermally induced cross-linking as described in the article by Cardoso et al referenced above, have all been claimed to improve the thermal stability of poly(ethyleneglycol).